This work involves the study of Mossbauer spectroscopy, at low temperatures and over a range of magnetic fields, of heme proteins and related model compounds. Emphasis is placed on hemoglobin and myoglobin and their physiologically relevant states, but work is contemplated on related proteins and related but non-physiological states. Work is in progess in several areas. The temperature dependence of quadrupole interaction and absorption line shape of a heme model has been measured and accounted for in terms of thermally induced relaxation of the oxygen molecule between different orientations. Similar work is in progress of hemoglobin and myoglobin. The state of deoxymyoglobin has been examined by means of Mossbauer measurements in high magnetic fields in the temperature range from 4.2 K to 195 K. The proportionality tensor between internal and applied magnetic field, and the sign and asymmetry parameter of the electric field gradient have been determined. In combination with published single-crytal Mossbauer measurements these have been interpreted to provide the orientation of the electric field gradient with respect to the heme plane. Future plans involve similar work on hemoglobin, and the development of a crystal field theoretical treatment to explain both. A program for calculating paramagnetic Mossbauer spectra of low symmetry low spin ferric materials has been developed and is being applied to heme protein azides and cyanides. BIBLIOGRAPHIC REFERENCES: Mossbauer Spectroscopy of Hemoglobin Model Compounds: Evidence for Conformational Excitation. K. Spartalian, G. Lang, J.P. Collman, R.R. Gagne, and C.A. Reed, J. Chem. Phys. 63 5375-82 (1975). Low Temperature Photodissociation Studies of Ferrous Hemoglobin and Myoglobin Complexes by Mossbauer Spectroscopy. K. Spartalian, G. Lang, and T. Yonetani, Biochim. Biophys. Acta 428 281 (1976).